Outline

Objective: The aim of this study was to adapt Ultrasonographic techniques first developed to show brain perfusion in cerebral ischemia to an intraoperative setting during surgery of low grade astrocytoma. The aim was to show the tumor and the surrounding brain tissue during brain tumor surgery by means of perfusion differences for online navigation and resection control. Ultrasound as a diagnostic tool in surgery of high-grade tumors and metastases has been shown already in former studies. With the underlying purpose we developed an algorithm using ultrasound contrast agent and were able to differentiate brain tissue and tumor as an online navigation tool.

Methods: Preoperatively a MRI with navigational setting was performed. After registration patients underwent several contrast-enhanced Ultrasonographic investigations (Phase Inversion Harmonic Imaging, bolus kinetic, fitted model function) during surgery. Off-line, time-intensity curves as well as perfusion maps were calculated and different analysis parameters, e.g. time to peak, peak intensity, peak width, were extracted to characterize perfusion and to detect the best analyzing parameter differentiating tumor tissue from normal brain.

Results: 5 patients with low-grade brain tumors (Gliomas WHO Grade 1 and 2) without contrast enhancement in MRI were investigated with contrast-enhanced ultrasonography during surgery. The contrast enhancement within the normal brain tissue was visible and tumor identification was possible by using peak width and time to peak analysis. Overall tissue differentiation with contrast agent was superior compared to conventional B-mode ultrasound imaging.

Conclusions: Intraoperative contrast-enhanced ultrasonography enabled visualization of low-grade brain tumors. Tumor borders could be displayed with this technique and the adequate analysis. Therefore this investigation could emerge to a low cost solution for intraoperative analysis and probably resection control in surgery of no contrast enhanced tumors.